The present invention relates to a digital speed control method which is particularly useful for controlling the speeds of motors used in a sectional drive system of a continuous processing line.
In certain types of sectional drive systems of a continuous processing line, such as a paper making machine, the motors of respective sections need to be operated in such a manner that there are precisely controlled differences, or draws, between the speeds of the motors, in order to maintain the quality of the products. Also it is desirable that the control system enables monitoring of the draws. Speed control systems used for these purposes are often called draw control systems.
To meet such requirements, it is known to use a proportional control as a minor loop and an integration control in an outer loop. A separate monitoring device has been employed to monitor the draws. Prior art systems are not sufficiently reliable and are bulky, as will be fully described later.